A number of vascular disorders, such as stroke, pulmonary embolism, peripheral thrombosis, and atherosclerosis, are characterized by formation of occlusions that prevent normal blood flow in blood vessels. For example, an ischemic stroke is a neurological dysfunction caused by a blockage of one of the major arteries of the brain. Hemodynamically significant restriction of arterial blood flow can lead to oxygen deprivation in tissue, referred to as ischemia, and can quickly lead to cell death and organ dysfunction. The brain is the organ most sensitive to ischemia, followed by the heart, the abdominal organs, and the extremities. The brain will usually not tolerate ischemia for very long without massive neuron death (stroke). When treating ischemic events in the brain, it is imperative to restore blood flow quickly and safely. The blockage can be the result of emboli or pieces of thrombotic tissue that have dislodged from other body sites (formed in the heart, carotid artery, or elsewhere) or from the cerebral vessels themselves. The emboli or pieces of thrombotic tissue may migrate downstream to occlude in the narrow cerebral arteries. The blockage may also be caused by the formation of a blood clot at the site of blockage (thrombosis) or the obliteration of the lumen of a blood vessel caused by atherosclerosis.
Stroke is the third most common cause of death in the United States and the most disabling neurologic disorder. Hemorrhagic stroke accounts for 20% of the annual stroke population. Hemorrhagic stroke often occurs due to rupture of an aneurysm or arteriovenous malformation bleeding into the brain tissue, resulting in cerebral infarction. The remaining 80% of the stroke population are ischemic strokes and are caused by occluded vessels that deprive the brain of oxygen-carrying blood.
When a patient presents with neurological deficit, a diagnostic hypothesis for the cause of stroke can be generated based on the patient's history, a review of stroke risk factors, and a neurologic examination. If an ischemic event is suspected, a clinician can tentatively assess whether the patient has a cardiogenic source of emboli, large artery extracranial or intracranial disease, small artery intraparenchymal disease, or a hematologic or other systemic disorder. A head CT scan is often performed to determine whether the patient has suffered an ischemic or hemorrhagic insult. Blood would be present on the CT scan in subarachnoid hemorrhage, intraparenchymal hematoma, or intraventricular hemorrhage.
Traditionally, emergent management of acute ischemic stroke consisted mainly of general supportive care, e.g., hydration, monitoring neurological status, blood pressure control, and/or anti-platelet or anti-coagulation therapy. In 1996, the Food and Drug Administration approved the use of Genentech Inc.'s thrombolytic drug, tissue plasminogen activator (t-PA) or ActivaseB, for treating acute stroke. However, the success rate of this approach is still very low. With this form of therapy, only 30% of patients are expected to realize a good or excellent clinical outcome several months following infusion, and patients who demonstrate signs of intracranial hemorrhage at the time of presentation (on a CT study of their heads) are not candidates for t-PA therapy. Also, intravenous t-PA therapy is associated with an almost 6% fatal intracranial hemorrhage rate.
Patients treated with t-PA were more likely to sustain a symptomatic intracerebral hemorrhage during the first 36 hours of treatment. The frequency of symptomatic hemorrhage increases when t-PA is administered beyond 3 hours from the onset of a stroke. Besides the time constraint in using t-PA in acute ischemic stroke, other contraindications include the following: if the patient has had a previous stroke or serious head trauma in the preceding 3 months, if the patient has a systolic blood pressure above 185 mm Hg or diastolic blood pressure above 110 mm Hg, if the patient requires aggressive treatment to reduce the blood pressure to the specified limits, if the patient is taking anticoagulants or has a propensity to hemorrhage, and/or if the patient has had a recent invasive surgical procedure. Therefore, only a small percentage of selected stroke patients are qualified to receive t-PA.
New classes of “neuroprotectant” agents and “angiogenesis promoters” are being developed and tested. These drugs may extend the effective therapeutic window for stroke therapy and permit better long term outcomes. Their use, however, may require novel delivery systems and often require that the patient be stabilized and ischemia relieved in order to obtain a lasting clinical improvement.
Obstructive emboli have also been mechanically removed from various sites in the vasculature for years. For example, the “Fogarty catheter” or variations thereof has been used, typically in the periphery, to remove clots from arteries found in legs and in arms. These well known devices are described, for example, in U.S. Pat. No. 3,435,826 to Fogarty and in U.S. Pat. No. 4,403,612 to Fogarty, each of which is incorporated by reference herein in its entirety. In general, these patents describe a balloon catheter in which a balloon material is longitudinally stretched when deflated. In procedures for removing emboli using the Fogarty catheter or other similar catheters, it is typical, first, to locate the clot using fluoroscopy. The embolectomy catheter is then inserted and directed to the clot. The distal tip of the balloon catheter is then carefully moved through the center of the clot. Once the balloon has passed through the distal side of the clot, the balloon is inflated. The balloon catheter is then gradually proximally withdrawn. The balloon, in this way, acts to pull the clot proximally ahead of the balloon to a point where it can be retrieved. The majority of procedures using a Fogarty type catheter repeat these steps until the pertinent vessel is cleared of clot material.
A variety of alternative emboli retrieval catheters have also been developed, in which various wire corkscrews and baskets must be advanced distally through the embolic material in order to achieve capture and removal. For example, Concentric Medical, Inc. (located in Mountain View, Calif.) has created an intraluminal clot retrieval system consisting of a nitinol-(Nickel-Titanium alloy) shape memory corkscrew-like coil that is advanced into an occluding clot, such as shown in U.S. Pat. No. 6,663,650; U.S. Pat. No. 6,730,104; and U.S. Pat. No. 7,285,126, each of which is incorporated by reference herein in its entirety. The coil and its attached wire are then withdrawn from the affected vessel, retrieving the thrombus material into a balloon-tipped guiding catheter positioned in the internal carotid artery. However, removal of emboli using such catheters carries potential problems. One such problem occurs when advancing the catheter through the clot dislodges material to a more remote site where removal may become more difficult or impossible.
New devices and methods are thus needed in treating vasculature occlusions in the body, including treating patients with acute ischemic stroke and occlusive cerebrovascular disease, and treating symptomatic patients with embolization or hemodynamic compromise. There are a number of significant problems faced in designing a system which will quickly and easily, yet effectively, evacuate emboli from a treatment location within a blood vessel. First, the small size of certain vessels in which such therapy occurs is a limiting factor in the design of emboli removal systems. Vessels as small as 3 mm in diameter are quite commonly found in the cerebral arteries, coronary arteries, and even certain saphenous vein graph bypass vessels can also be as small as 3 mm or 4 mm; although some can range as high as 7 mm. Nevertheless, a successful emboli removal system must be effective within extremely small working areas and safely traverse the tortuous cerebral vasculature. The system must also be equally effective in larger vessels, those of 5 mm or more in diameter.
Another obstacle is the wide variety in emboli dimensions. Although definitive studies are not available, it is believed that emboli may have approximate diameters ranging anywhere from tens of micrometers to a few hundred micrometers and lengths over 5 cm. More specifically, emboli that are considered dangerous to the patient may have diameters as large as 200 to 300 micrometers or even larger. Often obstruction removal systems have only a single capture device on the distal end to capture and contain the entire obstruction. Such a capture device must be of a relatively large size in order to effectively remove the entire source of vascular occlusion in one pass. However, the relatively large size of the single capture device may not accommodate small vessels.
Thus, an effective emboli removal system must be able to retrieve relatively large embolic particles and clots, at the same time, fit within relatively small vessels. In order to minimize the size of the obstruction removal system, the obstruction removal system of the present invention utilizes a plurality of relatively smaller capture devices that each capture a small portion of the clot or obstruction in order to remove the source of vascular occlusion in a piecemeal or gradual fashion.